We were also in the World the first of Dec last year, and I have no qualms about returning at the same time after our Pop Warner encounters.
As stated, I think they spend most of their time at WWOS. We did see players (only knew that because they had on shirts or hats stating so) behaving politely at DSMGM - the park I would say was were we saw the most of them.
The only other obvious group was cheerleaders and their moms at Epcot for Illuminations - the girls were fine and behaved.
We were at AKL, so didn't see any at the resort. I do believe it was the AllStars that had them, so even though we had no negative interactions, I would not stay there during this event (but I don't really choose to stay there at any time).
MVMCP was not a problem - but of course, this has a limited number of tickets so even if it had sold out, it wouldn't have been horrible.
Oh, also, I do believe that one night DSMGM had a party for those at Pop Warner but that was after normal park hours. We chose not to go to that park that day, thinking that they may head over early.